Pyroelectric infra-red detectors and detector arrays are used in a wide variety of applications and at operating frequencies ranging from just a few hertz to several kilohertz. Various materials have been used in this application ranging from TGS crystal through PVDF polymer to various ceramic formulations. The PZ family of ceramics. in particular, is widely used in thermal infra-red detector applications.
A significant improvement in signal-to-noise ratio can be achieved by the use of material which can be made to behave as a dielectric bolometer material, for example, lead scandium tantalate (Pb.sub.2 ScTaO.sub.6). Functionally very similar to a conventional pyroelectric material, the dielectric bolometer relies upon a pyroelectric response induced by a D.C. bias field typically with a magnitude of 1-5.times.10.sup.6 Vm.sup.-1. To provide an efficient detector, the bias field should be substantially uniform in magnitude throughout the volume of the detector material. Commonly dielectric bolometers can be fabricated from ceramic formulations which mechanically are very similar to conventional pyroelectric ceramics and allow similar processing techniques to be used mechanically to thin the materials and to define suitable electrodes.
The conventional approach to detector design is to define the detector by electrode patterning on the material surfaces. Normally, the electrodes consist of two areas defined on opposing faces of the detector material one of the electrode areas supporting some form of radiation absorber structure 20 as shown in FIG. 1 of the accompanying drawings. As shown, the detector structure requires electrical contacts 10,12 to be made to both faces 14,16 of the detector material 18. Two approaches to supporting linear array detector structures are through glue bonding the detector material to a support substrate or solder bonding using solder bumps to an interconnection substrate or readout circuit. With either technology it is difficult to contact both faces of the detector, particularly if the detector material has been reticulated to improve response and reduce thermal crosstalk between adjacent elements in an array. With a pyroelectric detector, this problem can be overcome by using a compensation region designed to cancel out common mode signals such as those caused by mechanical vibration or environmental temperature change. This region is connected in series opposition with the active element and requires electrical contacts to be made to one face of the detector only.
The pyroelectric ceramic is poled uniformly and this gives an output of opposite sign for the compensation region. Such an approach cannot, however, be applied to a dielectric bolometer where the response is induced by an applied field, if the same structure were to be used with two contacts a "compensation" region would then be acting in series complement rather than series opposition.